1. Field of the Invention:
The present invention relates, in general, to machine tools and, more specifically, to tool condition monitoring apparatus.
2. Background Description:
Tool monitoring systems have been devised which measure spindle power to determine the condition of tools. Prior art power-based tool monitors compare the spindle power profile to a set of fixed trip limits to determine whether a tool is broken (missing profile) or dull (excessive profile). If the power profile fails to reach a preset limit, such as a tool presence (TPL), during a machine cycle, a broken tool condition exists. When the power profile exceeds another preset limit, i.e., a dull tool limit (DTL), a dull tool condition exists. This scheme works well if there is only one tool to be monitored. In that case, a missing tool causes a complete absence of a normal power profile.
In a multiple tool application, however, the situation is more complicated. The power profile gets smaller; but does not completely disappear when one tool is missing. Any detection schemes that have relied on the fixed tool presence limit have proven to be inadequate in multiple tool situations. As tools get dull, the spindle power usage increases. As shown in FIG. 9, the power usage of three dull tools (one is missing, i.e. broken) is greater than that of four new tools (all tools are present). Therefore, a fixed tool presence limit that works for new tools fails to work for dull tools, and vice versa. This critical inadequacy has made traditional power-based tool monitors ineffective in multiple tool applications.
Thus, it is desirable to provide a tool monitor apparatus which is capable of monitoring tool conditions, such as a broken tool or a dull tool, in the multiple tool applications. It would also be desirable to provide a tool monitor apparatus which is capable of detecting one broken tool or one dull tool with a plurality of tools and a multiple tool application.